I would look for wiring defects first. P0571 = Brake pedal position sensor. Either the Brake pedal position sensor or the wiring. P0504 = ECM-510F Vehicle speed signal Diagnostic trouble code (DTC) information Condition Diagnostic trouble code (DTC) ECM-510F (no signal) is stored if there is no comm...

The brake pedal position sensor is essentially the same unit as fitted to the 850s and there was a write-up here on MVS on how to repair it. The casing is a little difficult to pry open but once done there is a small contact board at the top that needs to be re-soldered.

Don't worry, but unplug the battery before you remove the phone unit.
Cheers!